As is known, switching regulators provide a regulated output voltage to a load. The output voltage is regulated to be a substantially constant voltage irrespective of variations in the load and variations in the input voltage.
Conventional switching regulators have at least three configurations, including, but not limited to, a buck configuration, a boost configuration, and a buck-boost configuration. A conventional buck switching regulator provides a regulated output voltage in response to an input voltage that is higher than the regulated output voltage. A conventional boost switching regulator provides a regulated output voltage in response to an input voltage that is lower than the regulated output voltage. A conventional buck-boost switching regulator provides a regulated output voltage in response when input voltage that is higher, lower, and equal to the regulated output voltage.
Depending on configuration, a conventional switching regulator can have one or more electronic switches, an inductor coupled to the one or more electronic switches, and a capacitor coupled to an output node at which a regulated output voltage is generated. A conventional switching regulator also has a control circuit coupled in a feedback arrangement. Wherein the control circuit is coupled to receive the regulated output voltage, and, depending upon the sensed regulated output voltage, the control circuit is configured to generate one or more pulse width modulated (PWM) control signals having respective duty cycles proportional to a ratio between an input voltage to the switching regulator and the sensed regulated output voltage. The one or more control signals are used to turn on and of the one or more electronic switches, respectively.
It is known that n-channel field effect transistors (FETs) tend to have higher efficiency (i.e., lower drain-source resistance) than p-channel. FETs with the same integrated circuit area. Thus, conventional switching regulators tend to use n-channel FETs, and NMOS FETs in particular, as the one or more electronic switches, as opposed to p-channel FETs or PMOS FETs.
In order to switch to an on condition, an NMOS FET must have a gate-source voltage above a specified number of volts, for example, five volts. It will be apparent from discussion below that, for low input voltages, for example, three volts, conventional buck-boost switching regulators are unable to achieve a high enough gate-source voltage to turn on at least some of the one or more electronic switches, and thus, they are unable to regulate the output voltage for low input voltages.
It would be desirable to provide a buck-boost switching regulator that can operate at lower input voltages.